Lamp



A. J. SWEET April 23, 1940.

LAM P 3 Sheets-Sheet 1 @mio ZH @n om N 2 w o EZB En: l l, ON /l l fm om \\.,\A,// n 111// l//f Ov om INVENTOR Arthur J. Sweet BY W a. am

ATTORNEY A. J. SWEET April z3, 1940.

LAMP

Original FiledNov. 2'7, 1936 5 Sheets-Sheet 2 l ZENTTH mm- NoT Less THAN 9o Non mom-1 THAN |55 I-mN.- NoT Lass THAN 55 Nok MORE THAN 65 J- NoT Less THAN 45 Non MGRETHAN T55 T' NoT Less THAN 495 NOR MORE THAN 65 INVENTOR Arthur JS weet BY f4 /7 ATTORNEY April 23, 1940.

A. J. swEE-r LAMP Original Filed Nov. 27, 1936 3 Sheets-Sheet 3 INVENTOR Arthur J. Sweet BY a. 7D ATTORNEY N Abm Patented Apr. 23, 1940 new UNITEDSTATES PAT-ENT certes Application November 27, 1936, Serial No. 112,866

Renewed November 14, 1938 7 Claims.

This invention relates to illumination, and more especially to lamps in which an incandescent or arc source is contained within a bulb. In its more specic aspect the invention is di- 5 rected to the design and construction of lamps for use as elements of portable electric table and oor lamps.

One of the chief defects vof portable electric table or floor lamps" as heretofore available on l the market has been that the illumination on the l lamp. Thus the common 100 watt incandescent lamp in a typical portable lamp supporting the light center at a height of 18" above the working plane provides an illumination approximately as follows:

*220 37 ft.c. at 12 inches `from the axis 22 ft.c. at 18 inches from the axis 13 ft.c. at 24 inches from the axis 8 ft.c. 'at 30 inches from the axis Similar relationships, all exemplifying a considerable decrease in intensity of illumination as horizontal distance from the axis of the portable lamp increases, characterize alltypes of'portable lamps to-day available on the market. j

f3() It is the consensus o f competent opinion that ft.c.` to 25 ft.c. represents the lower limit of what is hygienically proper for the average reading task. Long-continued reading or similar use of the eyes at intensities on the work-mate- ;,35 rially lower than this involves an undue strain on the muscular system of the eye, a strain which will eventually cause permanent impairment of eye-sight. v y

Considerations offcost have generally deterred `40 the average user from providing a larger'bulb than 100 watts, or its equivalent in'two ormore bulbs of smaller size. To provide a hygienicallyadequate intensity of illumination, therefore, it has been necessary to hold the reading matter or '45 other Work within a distance of approximately 18" from the axis of the lamp. Under averagev therefore, generally impels the user to place his 55 Work at a point `where the'illumination is more tion at points close vto the axis of the portablev i0 llamp. Such over-brightv illumination adjacent to the work area reduces the efficiency with which the eye functions vand increases'the burden placed upon the muscular system of the eye.

Attempts have been made to correct this in- 15' herent deficiency of v-existing types of incandescent lamp by employing, inthe construction of the portable lamp, auxiliary light-controlling equipment. Such attemptshave thus farbeen successful in correcting'the above defect in only. '20 a very limited and inadequate degree.

rlhe most serious barrier totheI correction of the abovedefect by the employment of auxiliary reiiectors has been interference produced by the lamp bulb itself to the reflected light.H lny orderj`25 to provide the required lighting results,A such rel ectedlight has to be thrown' back upon the lamp bulb and to pass through it." With current shapes of bulb', a considerable 'portion of the reflected light impinges upon the bulb at such anro angle with the glass surface asto be partially reflected therefrom, with consequent 'interfer-4 ence Vwith ythe production of proper illumination results. While such bulb interference 4may be minimized by optimum optical design, there' isi`3'5 at present no known means of reducing itv tothe 'point where it becomes of little'or no practical importance. l

' It becomes highly desirable, therefore, to 'produce a lamp which, when mounted with lightfi0 center 15" to 18" above the Working p1ane,\will provide at a distance of from the axis an illumination substantially as great as that provided at a distance of 18". Indeed, it is desirable that the illumination at 30 be considerably greater than the illumination at 18", say twice as great: for if the printed paper or other 'object of vision be more or less specular, not

entirely matte, the same illuminationvwill be less effective, with respect to providing visibility, at 30" than at 18".

Expressing these requirements interms of light distribution, the desirableincandescent lamp for portable table or floor lamp use willbe one which Vemits at least 3 times, and ydesirablyx to 8 times, 55

supporting conductors 23 and 24.

as much light at an angle of 60 from the nadir as it does at an angle of 45 from the nadir. Previous to my invention no such lamp has been devised.

` One additional requirement of portable table or iioor lamp service calls for comment.

Table and oor lamps are frequently used without any other source of illumination within the room. If the illumination afforded by such portable lamp were provided exclusively on the work or adjacent thereto, the general surroundings in theroom would be illuminated only by light reilected by the work and adjacent areas, and hence would be but very dimly illuminated. Competent opinion is unanimous that extreme contrasts between the brightly lighted work and very dimly lighted surroundings is hygienically undesirable. The desirable incandescent lamp for portableI table or oor lamp use must, therefore, emit at least 20%, more typically 40 and under loccasional conditions of service asvmuch as 60% of its light inl a generally upward -direction where itwill'serve to aord a general illumination of the room` interior.

' With these general requirements in'mind, the nature of myinvention will be made clear from the following descrip-tion and drawings wherein:

Figure l is a graph showing the typical illumination on the-plane of the work afforded by existing types of-incandescent lampv when used,

without auxiliary*light-controlling equipment, in

table'orfloor lamp service, as compared with the ideal illumination andwith the farthest deviationfrom ythe ideal that can-be considered hygienically acceptable.

Y' Figure 2 is a constructional diagram showing the `significant elements A"and characteristics Awhich are involvedin application'of my-invention.

Figure'is an application of my'invention to a lamp designed for burning with base down (i. e toward thel nadir) Figure 4 is' an application of myinvention to a lamp designed for burning' with base up (i. e., toward the zenith).

yshown in Figure' 3, vthe `lamp comprises a -light-permeable-or vitreous envelope I0 having astem yI i integral therewith and terminating in av press l2 in whichare embedded a pair of rigid -supporting conductors i3 and i4. The distance Ibetween the'outerfportions of Isaid vconduct-ors is preferably asN great as practical. A ring type -coiled filament-I5 is connectedto thevendsl of the conductors I3 and Ill and is supported thereby. A' base li6 is connectedf-to'one end of the envelope and is electrically connected to said fa-stemf 2l integral therewith and terminating in af'press 22 in which areembedded a pair of rigid A vitreous arbor 25 is integralwith said stem and extends approximately along the longitudinal axis of said lamp. A coil ring type filament 2E is secured to the outer ends of said conductors 23 and 24. A

fpluralityof anchor wires 2'! are embedded in the outer end of saidarbor and are secured tov said 1 source at the apex of the angle.

' surface. 'being specular and the outer surface being either -ate between these two values.

filament 26 to help support the same. A base 28 is connected to the envelope and is electrically connected to the conductors 23 and 24.

The foregoing elements are old in the art, the essential features of my invention are being hereinafter set forth.

Referring equally to Figure 2, Figure 3, and Figure 4, my invention involves a contour of lamp bulb between a lower limit, A, not less than 55 nor-niore'fthan65 in `position and an upper 10 limit, B, not less than nor more than 135 in.

- position, all these angular values being measured from the nadir with the center of the light This contour of lamp bulb, A to B, is integral with a specular re- 15 flector 29 located on either its inner or its outer The-inner surface of said reflector 29 completelyaround-the bulbin surface of revolutionhavingthe lamp axis as its axis, or it may extend-onlya`v quarter ofl the way around the bulb, or it may extend to any degree intermedi- 25 In any event the reilector must be so located with respect to the envelope or bulb that its specularfor reflecting surfaceis located at least f as-closeto the source of light as the outer surface of said envelope "or' in other words the specu-' 30 lar/or reflecting'surface of the reiie'ctor is located no further from ythe source of light than the outer surface of said envelope.

Outside the above angular limits within which the contour of thelamp bulb must, to fall with- 35 in the `scope of my invention, be shaped as later herein set forth, the lamp bulb may take substantially whatevershape may best' be adapted to considerations of satisfactory operation of the ,lamp with minimum deterioration in lighteniit-40 ting qualities. However", that section' 'of the bulb, AC to A, lying labove the point where the internally reflected ray, RA from the lowest edge of the designed contour, A to B, passes out of the y lamp bulb', should desir'ably bewithinI 45 of per-2 5 `pendicular to the said 'reflected ray, RA save for such'minimum'distancebelow'A as maybe requiredto` passffrom the contour B4 to'Af to the contour A to C without involving undesirable strainswithin the structure 'of the glass. 1.50

It will be noted that myinvention involves a specific contour of'a portionoi :the light bulb in conjunction with ya denite position of` light source ratherA tlianany particular contour considered apart from such definite position of light 55 Proceeding to an exact definition of the reector which is preferably a portion of the bulb contour and which is thedenitive element 'of my invention, the following symbols are employed:

sis the angle, measured in degrees from the nadir with' apex at P, of the nadir segment of a vline drawn tangent to the reflecting contour at any point, P.

i is `the angle, measured in` degrees from the 65 Vnadirwithl apex at the center of the light source,

my invention is afforded by the formula ,.5

in which i will successively have values varying from a minimum value not less than 55 nor more than 65, both inclusive, to a maximum value not less than 90 nor more than 135, both inclusive; in which, at the minimum value of i, 1' is approximately equal to i and in which, at the maximum value of i, 1 has a value not less than 46 nor more than 52; and in which,l When T is greater than i, s is measured in a direction from the apex-nadir line opposite that in which i is measured.

The requirements of my invention would, indeed, be met if, at the minimum value of z', r had a value not less than 46 nor more than 52 and if, at the maximum value of 1l, T had a value approximately equal to the minimum value of i, the formula remaining valid and unchanged. However, such alternative values of r would produce a bulb form more difficult of manufacture and more liable to internal strains within the structure of the glass than would the preferred values.

The exact minimum value of i, lying between 55 and 65 inclusive, is determined by the maximum distance, measured in the working plane perpendicular to the axis of the lamp, at which it is desired to provide illumination from the lamp and by the distance, measured along the axis of the lamp, of the light center from this working plane. 'I'his minimum value of i is given by the formula Maximum distance of Work from axis Distance of light center from Working plane The exact maximum value of z', not less than 90 nor more than 135, is determined by the relative proportions of the generated light which it is desired to emit on each side of a plane perpendicular to the lamp axis and passing through the light center. It is never desirable to deliver more than 60% of the emitted light on the side of the plane opposite to that in which the reflecting contour A to B delivers its light; a value of 40% approximately represents the most gener'- ally desirable condition; While a value of 20% is the minimum. The exact determination of this percentage depends upon the relation which it is desired to provide between intensity` of illumination on the work and average intensity of i1- lumination of the room surroundings. The optimum value of this relation will vary as between the office and the home, the large roo-m and the small room, the light-nished room and the darknished room, and will also be materially inuenced by the size of the lamp employed. In general, the larger the room of typical use, the darker the finish, or the larger the size o-f lamp employed, the greater should be the percentage of light emitted on the side of the plane opposite to that in which the reflecting contour A to B delivers its light.

The above percentage of light having been decided upon, it becomes a simple matter fory one versed in the art so to locate the point B-that is, so to determine the maximum value of i-that the amount of light emitted between the maximum value of i and the zenith equals the desired percentage.

'Ihe maximum and minimum values of ihaving been determined as set forth above, a photometric test of the light-emitting element mounted at the center'of a spherical bulb will afford the data from which can be computed the amount of light which will fall uponthe reflecting surface -A tov B. This amount of light will be expressed in lumens.

The reflecting eiiiciency of the surface A to B being known, the amount of light which will be reflected by the surface may now be computed.

The ring-shaped section of the horizontal working plane within Which it is desired to provide illumination is now divided into a series of concentric rings. It is most convenient to choose the division points either 1 or 2 apart, depending upon the accuracy of design desired. The area of each of these concentric rings is now computed and expressed in square feet or decimal-fractions thereof.

The amount of direct light from the lightemitting element which falls upon each of the above concentric rings is now computed from the photometric test data referred to above. This amount of light will be expressed in lumens. The lumen sum for the entire group of concentric rings is next determined.

The illumination, expressed in foot candles, which it is desired to produce at the center of each concentric ring is now multiplied by the area of the ring, the product expressing the number of lumens which will be required to produce the desired illumination. The sum of these products will be the total amount of light required to produce the desired intensity of illumination at all points within the working area.

The sum of the direct lumens, obtained as specified above, and of the reflected lumens, obtained as specified above, gives the theoretical lumens available toproduce illumination in the working area. Were the light source a true point `Source, these theoretical lumens would correspond with the actual available lumens. Be-

cause the light source is not a true point source,v

there will be a certain spill at both the inner and outer edges of the ring-shaped area. The theoretical available llumens are therefore multiplied by a constant of the general order of magnitude of .9 to give the computed available lumens.

If the computed available lumens are greater or less than the required lumens, determined as specified above, the requirements must be suitably modiled or the lamp size altered, so as to bring the two Values into substantial agreement.

These initial steps having been taken, the designer is now in a position to determine exactly the contour A to B.

The zone A to B is divided into subzones each desirably about 4 wide.`

Starting at the middle of the subzonev whose lower limit is A, a point is taken which will provide a bulb of the desired diameter. It will `of course be understood that the diameter at this Apoint is very slightly less than the maximum bulb diameter.

The angular distance from the nadir of the center of the outermost concentric ring of the work area with respect to said point as the apex of the angle is now determined. This angle is the value of 1' in the designformula above given,

Proceeding from A toward B subzone by subzone, the above process is continued. When sufficient reflected lumens have been provided in the outermost concentric ring to produce, in con- V:sis

direct, downward lighting.

junction :with the direct lumens, 'the y'desired illumination, the angler is varied toconformto the center of the nextinner `concentric ring. This process is continued until thev innermost concentric ring and the subzone adjacent to B are coincidently reached. It will be found conducive to accuracy of design to make the subzones near B half the angular Width of the subzones employed over the larger part of the zonal area A to B.

The above design method provides a bulb contour and associated filament 'position entirely novel in the art of lamp manufacture. When this bulb contour A to B is provided with a specular reflecting finish, the resultant lampproduces a light distribution entirely novel, a distribution highly useful in certain specialized fields, such as that represented by portable table and floor lamps.

I do not, however, wish to be limited to the single application of portable table and floor lamp service. Incandescent lamps made in accordance with my invention will, used inverted, nd useful application in certain indirect lighting service. In such applications the ceiling becomes the working plane and the light emitted on the opposite side of the light center from thatin which the reflected light is emitted is used for There are other applications in which a lamp made in compliance withl my invention will be found Auniquely useful.

The effectiveness of my invention is enhanced by making the incandescent filament or other source of light of as small over-al1 physical dimensions as possible, that is, of as close an approximation as practical to a point source. This is particularly true of the vertical dimension. I prefer that the horizontal dimension does not exceed three-quarters of an inch and the vertical dimension does not exceed one-quarter of an inch. These approximate over-all values presuppose a lamp bulb having a diameter of approximately four inches, and will change proportionately with changes in bulb diameter.

In the preferred form of my invention I etch, frost, sand-blast or roughen all bulb areas not furnished with a specular reflecting finish. Such bulb areas may, however, be left smooth without violating the principle of my invention.

It is preferable though not essential to my invention to leave the center of the lamp bulb, on that side of the light center chiefly traversed by the reflected rays, free from any obstruction such as the glass arbor commonly used for mechanically supporting the filament in the ordinary construction of incandescent lamp. Instead, I prefer to use a single L-shaped support or a multiple of such L-shaped supports, the shorter bar of the L being adjacent to the light center and mounted approximately perpendicular to the axis of the lamp. Or, alternatively, I mechanically support the filament by the customary arbor construction but support that arbor from the opposite side of the light center from that chiefly traversed by the reected rays.

velope, the lower limitof the major portion of said reflector being not less than fifty-five degrees nor more than sixty-rive degrees and the upper limit of the major portion of said reflector being not less than ninety degrees nor more than one hundred and thirty-five degrees, all of said angles measured from the nadir with the apex of each angle. at the center of said source of light, the contour of said reflecting surface and its position with respect to said source being such that the illumination on a horizontal plane produced by the light so reflected is substantially non-decreasing as the horizontal distance from a Vertical axis through the center of the light source increases until reaching the maximum working distance for which the lamp is designed, beyond which distance said illumination rapidly decreases.

2. A lamp comprising a light-permeable envelope, a source of light located therein and a rellector, the inner surface of said reflector be" ing specular and located at least as close to the center of said light source as the outer surface of said envelope, a limit of the greater part of said specular surface being not less than fiftyve degrees nor more than sixty-five degrees and another limit of said greater part of said specular surface being not less than ninety degrees nor more than one hundred and thirty-five degrees, all of said angles measured from the nadir with the apex of each angle at the center of said light source, the contour of said reflecting surface and its position with respect to said source being such that the illumination on a horizontal plane producedby the llight so reflected increases as the horizontal distance from-*the vertical axis vthrough the light source increases until the maximum Working distance for which the lamp is designed is reached, beyond which distance said illumination rapidly decreases, the greater part of that portion of the envelope in the paths of the reflected rays and on the opposite side of the envelope being not less than forty-rive degrees nor-more than one hundred and thirty-five degrees to the paths of said rays as they strike said portion.

3. A lamp comprising a light permeable envelope, a source of light therein anda reflector, said reflector located Anot further from said source of light than the outer surface of said envelope, the contour of the inner surface of said reilector and its position with respect to the center ofv said source of light being in approximate conformity with the equation s=1/(z'-r) in which S is the slope of the inner reflecting contour of the reflector at any-particular point thereonmeasured in angular degrees from the nadir; i is the angle, measured, in degrees from the nadir, of a line drawn from the center of said light source to said particular point; the minimum Value of i being between fty-ve degrees and sixty-five degrees, both inclusive, and the maximum value of i being between ninety degrees and one hundred and thirty-five degrees, both inclusive; r is the angle, measured in degrees from the nadir, at which it is desired to reflect the light, r being approximately equal to i at the minimum value of i and being not less than forty-five degrees nor more than fifty-two degrees at the maximum value of i.

4. A lamp comprising a source of light within a light-permeable envelope, the contour of said envelope between a minimum angle not less than fifty-five degrees nor more than sixty-five degrees and a maximum angle not less than ninety degrees nor more thanone hundred thirtyf`1ve degrees, said angles being measured from the nadir with apex of angle at the center of the source of light, being such that, when a specular reilecting surface is applied thereto, the illumination on a horizontal plane `produced by the light reflected therefrom is substantially nondecreasing as the horizontal distance from the vertical axis through the center of the light source increases.

5. A lamp comprising a source of light, a lightpermeable envelope and a specular reflector lo-A cated between the light source and the envelope, the contour of said reflector between a minimum angle not less than fty-i'lve degrees nor more than sixty-live degrees and a maximum angle not less than ninety degrees nor more than one hundredy thirty-five degrees, said angles being measured from the nadir with apex of angle at the center of the source of light, being such that the illumination on a horizontal plane produced by the light reflected therefrom is substantially non-decreasing as the horizontal distance from the vertical axis through the center of the light source increases.

6. A lamp comprising a source of light Within a light-permeable envelope, a portion of said envelope having an inner-directed specular reflecting surface applied thereto and having a contour in substantial 'conformity With the equation s=1/2(z'-r) in which s is the slope, measured in angular degrees from the nadir, of said contour at any point thereon; i is the angle, measured in degrees from the nadir, of a line drawn from the center of said light source to said point; the minimum Value of i being not less than iifty-ve degrees nor more than sixty-five degrees and the maximum value of i being notv less than ninety degrees nor more than one hunr is the angle,`

than forty-six degrees nor more than sixty-five degrees and being so chosen that the illumination on a horizontal plane produced by the light reilectecl by said specular reflecting surface is substantially non-decreasing as the horizontal distance from the vertical axis through the' center of the light source increases.

7. A lamp comprising a light permeable envelope, a source of vlight therein and a reflector, said reflector located not further from said source of light than the outer surface of rsaid envelope, the contour of the inner surface of said reflector and its position with respect to the center of said source of light being in approximate conformity with the equation S=1(i-1') in which S is the slope of the inner reilecting contour of the reflector at any particular point thereon measured in angular degrees from the nadir; i is the angle, measured, in degrees from the nadir, of a line drawn from the center of said light source lto said particular point; the minimum value of i being between fifty-five de-v grees and sixty-iive degrees, both inclusive, and the maximum value of i being not less than ninety degrees; 1' is the angle, measured in degrees from the nadir, at which it is desired to reflect the light, r being approximately equal to -z' at the minimum value of i and being not less ARTHUR J. SWEET.` 

